Oldest marsupial discovered

Reconstruction of Sinodelphys szalayi as an agile climber. The blue background indicates that the nocturnal animal was active around dawn and dusk. This mammal was about 15 centimeters (six -- inches) long and weiged about 30 grams (one ounce).
Illustration courtesy of Mark A. Klingler/CMNH.
Click here for a high resolution photograph.

Scientists recently found fossil bones of the oldest-known relatives of kangaroos, koalas, opossums and the other "marsupials" -- mammals that carry their tiny babies in pouches.

The scientists who found the fossils in northeast China say the extinct, mouse-sized marsupial lived about 125 million years ago, when dinosaurs still ruled the Earth. That's 50 million years older than the next-oldest fossil of a pouch-packing marsupial.

Many extinct mammals are known from just a few bits of teeth or bone, but the Chinese fossils form a nearly complete skeleton. This allows scientists to learn a lot about how the animals lived. For example, the foot bones show that it could probably climb trees, which may have allowed it to live where other mammals could not.

Zhe-Xi Luo, an author of the study who works at the Carnegie Museum of Natural History in Pittsburgh, PA, and Nanjing University in Nanjing, China, believes that the new fossil, along with others found in the same area, suggests that many different mammals evolved in Asia. But others mammal scientists say that we need to find and study many more ancient mammal fossils before we can say where in the world different mammals originated.

The findings appear in the 12 December 2003 issue of the journal Science, published by AAAS, the non-profit science society.